The present disclosure relates generally to integrated circuit device fabrication, and more specifically, to a method of adding a metal stud in an integrated circuit structure to serve as a grain boundary diffusion barrier.
Integrated circuits are typically fabricated with multiple levels of patterned metallization lines, electrically separated from one another by interlayer dielectrics containing vias at selected locations to provide electrical connections between levels of the patterned metallization lines. As these integrated circuits are scaled to smaller dimensions in a continual effort to provide increased density and performance (e.g., by increasing device speed and providing greater circuit functionality within a given area chip), the interconnect linewidth dimension becomes increasingly narrow, which in turn renders them more susceptible to deleterious effects such as electromigration.
Electromigration is a term referring to the phenomenon of mass transport of metallic atoms (e.g., copper or aluminum) which make up the interconnect material, as a result of unidirectional or DC electrical current conduction therethrough. More specifically, the electron current collides with the diffusing metal atoms, thereby pushing them in the direction of electron current travel. Over an extended period of time, the depletion of metal at the cathode end creates local tensile stress to form voids in the metal to cause line resistance increase or even open circuit. On the other hand, the accumulation of metal at the anode end of the interconnect material significantly increases the local mechanical stress in the system. This in turn may lead to delamination, cracking, and even metal extrusion from the metal wire, thereby causing an electrical short to adjacent interconnects. Electromigration becomes increasingly more significant in integrated circuit design as relative current densities through metallization lines continue to increase while the linewidth dimensions shrink.
For very fine copper lines, copper grain growth, especially at the lower portion of the trench, has been a challenge. Relatively high temperature anneal was found not very effective to promote those fine grains to grow. As a result, very fine grains exist, especially along the lower portion of the trench. Those grain boundaries serve as fast copper diffusion path to cause electromigration and stress migration degradation. Both electromigration and stress migration are mechanisms that degrade the reliability of the semiconductor device and are therefore important parameters for the design of semiconductor devices. A solution is needed to block those fast copper diffusion paths in order to maintain the fine metal line reliability.